In Episode 52, faithfully transcribed here, they talked about 'Clams' or lines that of dialogue that are extremely cliched. They went through a huge long list, many of which mainly applied to action movies, but quite a few applied to sitcoms. And I thought it would be interesting to name and shame those lines here.
But one comment first. Here is the problem. Your dialogue needs to be real and believable. We are a society that is heavily influenced by television and movies - and now people say lines that are very common in movies. One of the most tiresome of these is "I could tell you but then I'd have to kill you." I'm sure it was an original line once but it's been duplicated and rehashed so many times that now it's only ever meant as a lame joke. Your job, as a sitcom writer, is to write dialogue that's funny, relevant, original and, crucially, in character.
In researching Bluestone 42, Richard and I talked to soldiers not just for stories and accuracy, but to hear how they talked. We found that soldiers had picked up a lot of catchphrases from the TV comedy. For example, they would talk about 'cunning plans' - obviously quoting Baldrick from Blackadder. We just couldn't have our characters use phrases like that, even if they were realistic. We had to come up with a way of talking which felt real and truthful, but was also original. Hopefully, we succeeded in that. (Soldiers tell us we did, which is nice.)
So, let's make a start on this list.
The Legacy of Chandler Bing
'Did I just say that out loud?' Yes, Chandler Bing, you did. And now everyone says it. Even in other sitcom scripts that I read. I think this line is from the first ever episode of Friends. Even if it weren't from a sitcom, it just sounds second hand now. The same goes for 'Don't even go there' and 'Too much information' or variants like 'That was more than I needed to know'. We know in our hearts these are hack, second-hand lines. They should never appear in our scripts, even though people still use those phrases in every day life.
'You make that sound like it's a bad thing' is a little more recent, but we're done with this now too, aren't we? I know it's funny when Gene Hunt says it in Life on Mars. But let's retire this one too. Along with 'I just threw up a bit in mouth' or the more British 'I just did a bit of sick in mouth'. It's no longer original. And there's the variant of this line at times of happiness or laughter - “I did a bit of wee, just then”. Again, we're done with this.
Stuff your Dad would day
Then there are weak conversational lines like 'We have to stop meeting like this'. It's the kind of thing your parents would say passing someone on the stairs. See also 'Don't call us, we'll call you' and '[abstract noun] is my middle name (unless you're Austin Powers).
Arguments throw up plenty of well-worn cliche's, like “You give [thing] a bad name”. And “Calling you a [thing] is an insult to [slightly larger category of thing].” Then the line of incredulity: “What part of [key thing] don’t you understand?”
Undermining Your Reality
Then there are lines that acknowledge that we're in sitcom and it's early in the episode and nothing big has gone wrong yet. e.g. 'What could possibly go wrong?' or 'How hard can it be?' And '“No, no, no, no, no, no, I’m not going to do the thing.” And then we cut to: Them doing the thing. And then after the calamity, explosion or catastrophe, our hero says 'That went well.' Although the audience know it's a sitcom and know it's not real, they are happy to suspend their disbelief while you tell a story. Clanging bells with lines that undermine the realism of the genre just don't help. Your writer friends might think its clever or ironic, but the vast majority of the audience really don't care.
There are other ways of undermining the realism by having your characters quote cliches from movies - but in the right context thanks to the story of your sitcom, and then they say 'I've always wanted to say that.' Or they have something cool they get to use for a little while and then say 'I've got to get me one of these' (which Will Smith says in Independence Day when he flies off at great speed in his super-fast Mac Compatible space ship). Or quoting the First Rule of Fight Club. Please stop now.
And finally, there are jokes like 'He's behind me, isn't he?' Unless you have a really good twist on this (We sort of did one of these about 12 minutes in to Episode 8 of Bluestone 42), or any of the above, avoid them. Give it a few more minutes. Delete it and force yourself to come up with something better. And if your characters seem to keep spouting cliches, rather than have a voice of their own, you might want to go back and redefine your characters.